The Digestive System The process of digestion has 5 functions: Ingestion: Digestion: taking food into the body breakdown of insoluble
substances into soluble ones Absorption: uptake of soluble substances into cells Assimilation: Egestion: how cells use food
removal of undigested waste Digestion Egestion faeces Ingestion Absorption
Food is broken down into smaller pieces by biting, chewing, churning, bile action. These pieces are not soluble but have a large surface area for enzymes to work on. 2cm
Surface area = 24 cm2 Volume = 8 cm3 2cm 2cm SA : V ratio = 24:8 = 3:1
Surface area = 6 cm2 1cm 1cm 1cm Volume = 1 cm3
SA : V ratio = 6:1 Enzymes break chemical bonds to make insoluble food particles soluble. Carbohydrases break down carbohydrates into sugars Proteases break down proteins into amino acids
Lipases break down fats (lipids) into fatty acids and glycerol model gut experime nt boiling tube What do you
remember Add gall bladder, bile duct, sphincter Buccal cavity Salivary gland Oesophagus Liver
Stomach Duodenum Pancreas Ileum Colon Appendix
Anus Rectum Mechanical: chewing, biting Chemical: Saliva from the salivary glands
contains the enzyme CARBOHYDRASE. Starch + carbohydrase sugar (maltose) The ball of food is called a bolus NO FOOD IS BROKEN DOWN HERE Muscles in the wall of the oesophagus contract, pushing food down to the
stomach. This is called PERISTALSIS peristalsis Muscles in wall contract FOOD
PERISTALSIS Oesophagus wall Food moves forwards The strong muscle walls contract to churn and mix food with stomach
juices called GASTRIC JUICES. Cells in the stomach wall produce a protease enzyme that digests proteins, breaking them down into amino acids. The stomach cells also produce hydrochloric acid HCl, which
Lowers the pH for the protease enzyme to work Kills bacteria Stops salivary amylase from working A circular, sphincter muscle at the exit of the stomach opens to allow food into the small intestine. It controls release of food from the stomach.
Bile, made in the liver and stored in the gall bladder passes along the bile duct into the duodenum. Bile breaks fats into very small droplets, increasing the surface area for enzymes to work on. This is called emulsification. Bile is alkaline and therefore also neutralises acid from the stomach.
bile made in the liver passes into the gall bladder gall bladder digestive enzymes produced in pancreas bile duct
pancreatic duct duodenum ENZYMES are added to the duodenum from: The pancreas The wall of the duodenum
Carbohydrases break down starch to sugars Proteases break down protein to amino acids Lipase breaks down fat to fatty acids and glycerol Main function is absorption. The walls are adapted for efficient diffusion of the soluble products of digestion.
ridge covered with villi network of blood capillaries lacteal absorbs fatty acids
villus muscl e layer arteriole venuole
A villus sugar ileum wall amino acids fatty acids blood
capillaries lacteal to liver Long length (5m), folds and villi increase the surface area for absorption Villi contain blood vessels to carry away absorbed nutrients
Villi contain lacteals to carry away absorbed fats The walls are thin, one cell thick, and permeable to form a short diffusion distance The absorbed nutrients, amino acids and sugars are carried in the blood to the liver in the
HEPATIC PORTAL VEIN. NO DIGESTION OCCURS HERE The colon has a large surface area for the absorption of water from the fluid we drink, food we eat, mucus and digestive juices. It also absorbs mineral salts.
Solid waste made up of undigested food, bacteria and cells from the gut forms faeces, which is stored in the rectum before passing out of the body through the anus.
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